Amino Acid Residues in the Putative Transmembrane Domain 11 of Human Organic Anion Transporting Polypeptide 1B1 Dictate Transporter Substrate Binding, Stability, and Trafficking

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• 作者：Weifang Hong ; Zhixuan Wu ; Zihui Fang ; Jiujiu Huang ; Hong Huang ; Mei Hong
• 刊名：Molecular Pharmaceutics
• 出版年：2015
• 出版时间：December 7, 2015
• 年：2015
• 卷：12
• 期：12
• 页码：4270-4276
• 全文大小：365K
• ISSN：1543-8392

文摘

Organic anion transporting polypeptides (OATPs, gene symbol SLCO) are membrane proteins that mediate the sodium-independent transport of a wide range of endogenous and exogenous compounds. Due to their broad substrate specificity, wide tissue distribution, and involvement in drug鈥揹rug interactions, OATPs have been considered as key players in drug absorption, distribution, and excretion. Transmembrane domains (TMs) are crucial structural features involved in proper functions of many transporters. According to computer-based modeling and previous studies of our laboratory and others, TM11 of OATP1B1 may face the substrate interaction pocket and thus play an important role in the transport function of the protein. Alanine-scanning of the transmembrane domain identified seven critical amino acid residues within the region. Further analysis revealed that alanine substitution of these residues resulted in reduced protein stability, which led to significantly decreased protein expression on the plasma membrane. In addition, all mutants exhibited an altered K_m for ES uptake (either high affinity or low affinity component, or both), though K_m for taurocholate transport only changed in R580A, G584A, and F591A. These results suggested that critical residues in TM11 not only affect protein stability of the transporter, but its interaction with substrates as well. The identification of seven essential residues out of 21 TM amino acids highlighted the importance of this transmembrane domain in the proper function of OATP1B1.